The present invention relates generally to color cathode-ray tubes for use with color display devices, such as color television sets and computer monitors or the like; and, more particularly, the invention relates to those color cathode-ray tubes having an electron gun assembly with an improved electrode configuration provided inside of the color, cathode-ray tubes.
To enable attainment of a high resolution, while retaining good focus characteristics, over the entire area on the screen faceplate, electron guns for use in cathode-ray tubes, such as Brawn tubes for television sets and Brawn tubes for computer display monitors, are required to optimally control the beam spot shape in accordance with the amount of beam deflection.
One prior known electron gun of this type has been disclosed in, for example, Japanese Patent Laid-Open Hei 04-43532 (1992).
The electron gun as disclosed by the above-identified publication is arranged to include first electrode means for generating a plurality of electron beams and for allowing these electron beams to travel along mutually parallel initial paths on a horizontal plane to reach a screen, and second electrode means constituting a main lens used for focusing each electron beam onto the screen. In this electron gun, a certain focus electrode, selected from among those electrodes making up the main lens and neighboring upon an acceleration electrode with a maximum voltage applied thereto, is subdivided into a plurality of electrode members, wherein the focus electrode comprises an electron lens of a first kind for use in applying a voltage which is variable in synchronism with the deflection of at least one electron beam to thereby cause the electron beam cross-section or profile to change into a non-axial symmetrical shape with an increase in the deflection amount, and the focus electrode also comprises an electron lens of a second kind having a lens intensity that becomes weaker with an increase in deflection amount of the electron beam upon application of a voltage variable in synchronism with the deflection of the electron beam. The main lens, made up of the acceleration electrode and the focus electrode have a focusing action, with respect to the electron beam, which is stronger in the horizontal direction than in the vertical direction.
In the electron gun described above, by subdividing the focus electrode that neighbors the acceleration electrode into a plurality of electrode members and also providing therein at least one electron lens of the first kind for applying to the electrode members a voltage variable in synchronism with the deflection of an electron beam, to thereby cause the profile of such electron beam to change with an increase in the deflection amount into a non-axial symmetrical shape, and, in addition thereto, also providing at least one electron lens of the second kind for applying a voltage variable in synchronism with deflection of the electron beam to thereby weaken its lens intensity with an increase in deflection amount of the electron beam, while employing an arrangement that causes the main lens formed of the acceleration electrode and focus electrode to have its focusing action stronger in the horizontal direction than in the vertical direction, an arrangement is provided wherein the first-kind electron lens will change the profile of the electron beam in a laterally long direction to thereby correct astigmatism due to deflection, while allowing the second-kind electron lens and the main lens to change in lens intensity for correction of the curvature-of-field.
In addition, at the center of the screen, a focus action which is stronger in the horizontal direction than in the vertical direction of the main lens and a focus action which is stronger in the vertical direction than in the horizontal direction of the first-kind electron lens will cancel each other, thus enabling the electron beam to form a nearly circular beam shape.
However, in view of the fact that television sets and display monitors have been experiencing demands for reduced weight and downsizing, as well as low power dissipation or the like in recent years, it should be required in order to reduce the loads of cathode-ray tube drive circuitry to maximally reduce the voltages that increase in potential with an increase in deflection. To this end, the above-noted prior art calls for designing the first-kind electron lens so that its lens intensity is as strong as possible, which would result in the first-kind electron lens forcing the electron beam profile to change to become horizontally longer excessively. Especially, as in large-current regions, an electron beam hitting the main lens can become too large in diameter in the horizontal direction resulting in the electron beam attempting to travel on the outer side of the main lens, the electron beam can receive significant influence from a spherical aberration of the main lens, which in turn causes the horizontal diameter to become larger relative to that in the vertical direction. This results in creation of a problem as to horizontal image resolution reduction which precludes achievement of good image quality.
It is therefore an object of the present invention to provide a color cathode-ray tube which is capable of suppressing an increase in the horizontal diameter of more than one electron beam emitted from an electron gun to thereby obtain good image quality over the entire area of a display screen.
To attain the foregoing object, the present invention employs a specific arrangement.
A color cathode-ray tube comprises a screen, an electron gun having three cathodes arranged on a single horizontal plane for generation of electron beams, first electrode means including a control electrode and a first acceleration electrode disposed sequentially from the cathodes for causing the electron beams to travel to the screen along initial pathways parallel to each other on the single horizontal plane, and an electron gun having second electrode means including a focus electrode and a final acceleration electrode for forming a main lens for use in focusing the electron beams on the screen picture plane, wherein
those electrodes constituting the second electrode means of said electron gun include a focus electrode neighboring upon the final acceleration electrode with a maximum voltage applied thereto and being made up of a plurality of divided electrode members, the cathode-ray tube comprising:
a final-stage main lens formed of said final acceleration electrode and an electrode member neighboring upon this final acceleration electrode for providing a focusing action which is stronger in a horizontal direction than in a vertical direction when all the electrode members constituting said focus electrode as subdivided into a plurality of parts are equal in voltage potential;
at least one electron lens of a first kind formed between said divided focus electrode members for having a focusing action stronger in the vertical direction than in the horizontal direction and for causing the electron beams to change in profile with an increase in deflection amount thereof by applying a voltage potentially variable in synchronism with deflection of the electron beams;
at least one electron lens of a second kind formed between said divided focus electrode members for weakening the lens intensity with an increase in deflection amount of the electron beams by applying thereto a voltage variable in synchronism with deflection of the electron beams; and
an electron lens of a third kind formed of at least one electrode constituting the first electrode means of said electron gun for having a focusing action stronger in the horizontal direction than in the vertical direction.
With such an arrangement, the following effect is obtainable.
By providing the third-kind electron lens for longitudinally deforming the electron beam cross-sectional shape or profile as formed between at least one electrode and another electrode adjacent thereto, which are selected from among those electrodes making up the first electrode means, it becomes possible to suppress an excessive horizontal expansion of more than one electron beam due to action of the first-kind electron lens, which in turn makes it possible to reduce the spherical aberration in the horizontal direction that the electron might receive in the main lens. As a result, it is possible to downsize or miniaturize the horizontal diameter of an electron beam spot at the center of the display screen, thereby enabling achievement of excellent image quality over the entire screen area.